Long-term trends in radiation brightening in the United States during 1995–2010
Authors
Chuen Meei Gan — National Exposure Research Laboratory
Jia Xing — U.S. Environmental Protection Agency
Jonathan Edward Pleim — U.S. Environmental Protection Agency
Rohit Mathur — U.S. Environmental Protection Agency
Chuck N. Long — NOAA- Earth System Research Laboratory
Chao Wei — U.S. Nuclear Regulatory Commission
Francis S Binkowski — University of North Carolina, Chapel Hill
Category
Aerosol-Cloud-Radiation Interactions
Description
Long-term surface observations (1995–2010) of shortwave radiation, aerosol optical depth (AOD) and aerosol concentration from several networks (SURFRAD, CASTNET, IMPROVE, and ARM) in the U.S. are analyzed to infer the association between trends in tropospheric aerosol burden and radiation across the country. Seven regions with varying climatology are selected in this assessment to better understand the spatial and temporal distributions of aerosols and clouds in conjunction with their direct, semi-direct, and indirect effects on radiation. A well-constructed emission data set from Xing et al. (2012) is used to verify the hypothesis that the reductions in anthropogenic aerosol burden resulting from substantial reductions in emissions of sulfur dioxide and nitrogen oxides over the past 15 years across the U.S. has caused an increase in shortwave (SW) radiation near surface. The trend analysis indicates a SW radiation "brightening," particularly in the eastern U.S. However, this phenomenon is less pronounced in the western U.S., since many of the Clean Air Act (CAA) control measures were aimed at coal-fired power plants that are more prevalent in the eastern U.S. Moreover, these locations could be influenced by local terrain influences as well as episodic long-range pollution transport, which may contribute to the lack of a clear association between trends in aerosol burden and surface radiation at these locations. The existence of a strong association between trends in surface solar radiation and aerosol burden provide a unique test for current generation of climate-chemistry models. Multi-decadal model calculations with the coupled Weather Research and Forecasting Community Multi-scale Air Quality Model (WRF-CMAQ) model (Wong et al. 2012) are being set up for the 1990–2010 period to test the ability of the model to simulate not only the changes in aerosol burden over the U.S. arising from the implementation of the CAA, but also the associated radiation brightening as indicated in the present analysis. The results of the analysis will be presented together with the emission trends in the poster. Early results from the modeling studies and their comparison with the trends inferred from the observations will be reported in a companion poster by Wei et al.
